How can I protect my addon code from scammers?
Especially if it's targeted to a specific community, your best shot (IMO) would be to advertise what you are doing as widely as possible. Post about your addon in forums, on your homepage/blog (if you have...), maybe also Blender Market etc. as early and transparently as possible.
Then, whenever you encounter one of the scammers trying to make money of your code, put out a comment linking to your original post and tell everybody that they can get the same value for free.
Spreading knowledge about your work helps others to spot such fraudulent offers early.
Having traceable proof of your original code ownership might come handy if some of the scammers turn real nasty and try legal action.
Other that that, I dont't think that you have a real chance by obfuscating your code. All you do is make life difficult for yourself and the legitimate users.
P.S: You might find this an interesting read in the context: https://www.blender.org/press/re-branding-blender/